The present invention relates to a radiation hardened active “OR” circuit.
Certain electronic applications use two or more independent voltage sources to improve reliability. In the event of one of the power sources dropping out or becoming too low to operate the load circuitry, the load is powered by a second source. Many such applications are designed for use in satellites and spacecraft. In these applications, function must operate in the presence of high radiation levels.
As shown in FIG. 1, a simple diode OR circuit 1 is shown. A simple diode OR circuit 1 can be implemented by connecting two power sources 2, 3 to the load 6 through two rectifiers 4, 5. The higher magnitude of the two voltage sources 2, 3 supplies the load 6 while current is not allowed to be fed to the lower magnitude voltage source. This type of connection is termed a “redundant” arrangement. The connection of two voltage sources 2, 3 to two rectifiers 4, 5 with a common output 6 is termed an “OR” or “diode OR” circuit.
There are two significant drawbacks to the diode OR circuit 1. One drawback is the power loss associated with the voltage drop across the rectifier that is conducting current. A second drawback is that a voltage sources doesn't always fail by reducing or dropping out, but may instead fail by increasing in magnitude. In the latter instance, instead of the application being more reliable due to the use of the diode OR, the diode OR may allow a potentially damaging over-voltage to be applied to the load. Furthermore, when a simple diode OR circuit is used for low voltage, high current applications, the resultant power and voltage drop may be intolerable.